The objective of this research is to investigate functions of key regulatory genes in axial regionalization during development of multicellular animals. This objective falls within the long-range comprehensive goal of addressing fundamental questions of molecular patterning mechanisms in metazoans. In this study, we will use functional genetic assays to determine the roles of the Hox/ParaHox genes in axial patterning in cnidarians. The conserved function of HoxlParaHox genes in anterioposterior patterning of triploblastic animals defines the bilaterian 'zootype'. Whether these genes perform comparable roles in cnidarians remains to be determined. There are several specific aims. In this proposed study. First, a posterior ParaHox gene will be isolated from Nematostella vectensis (Cnidaria: Anthozoa) and its expression pattern characterized. Next, the function of cnidarian Hox/ParaHox genes during development will be examined in N. vectensis using two complementary functional assays, ectopic gene expression and gene silencing. Finally, the function of cnidarian Hox/ParaHox genes during the process of regeneration will be examined to elucidate potential homology between the mechanistic events in ontogeny and regeneration. Determining Hox/ParaHox gene function in cnidarians will allow us to establish axial homologies between cnidarians and bilaterians. These results will reveal the ancestral roles of Hox and ParaHox genes in early metazoan history and will provide valuable insight to the evolution of complex body plans.